Production Of The Microcrystalline Cellulose From Rice Straw And Probable Reactions Occurred In The Progress Of Acid Hydrolysis

Microcrystalline cellulose owns a wide range of applications in the field ofmedicine, chemical industry, light industry and agriculture. At present, the most ofraw material of used to produce microcrystalline cellulose are cotton fiber and wood,their price is very expensive and the resource is limited. The biomass of rice strawcontaining35%to40%cellulose, amount available, and is a potential source ofcellulose for microcrystalline cellulose production. But rice straw also containsabout20%lignin and25%hemicellulose, they are built up a dense network structureso that limit its development and application in the field of microcrystalline celluloseseverely. For product qualified microcrystalline cellulose from rice straw, somepretreatment to the rice straw are must be needed. Therefore, this study aimed toselection a suitable pretreatment method, and then optimized conditions, studied thepretreatment mechanism to the rice straw and the probable reactions in the processof acid hydrolysis to the wood fiber, the mainly research include the followingpoints:(1) At the first, we investigated the possibility that product MCC from rice strawin the four pretreatment methods (SO3, NH3, SO3/NH3and NH3/SO3combine dilutealkali for pretreatment rice straw), and found that the best preparation method wasthat the rice straw firstly micro-thermal exploded with sulfur trioxide, then treatedwith ammonia, soon after the pretreatment straw caustic by dilute alkali, acidhydrolysis and bleaching. While we selected the cellulose content and yield as thetargets for optimal the processes, after analysis, the optimal conditions is the liquidratio between rice straw and SO3was1:4, temperature70℃, treat90min; the liquidratio between rice straw and NH3is1:20, temperature60℃, treat120min; the liquidratio between rice straw and NaOH was1:15, temperature90℃, treat120min. In theoptimal conditions, the content of straw microcrystalline cellulose is large to98.3%and the yield was30.2%.(2) We employed the technologies of FI-TR, XPS, XRD and SEM to study thepretreatment mechanisms to rice straw by SO3/NH3combine dilute alkali, andfounded that rice straw may had the esterification reaction with SO3in the process ofmicro-thermal explosion. The lignin of straw and NH3may have chemical reactionand damage its structure so that promoting the lignin removed, but the both methodswere failed to achieve the requirements of microcrystalline cellulose. We also founded that the synergistic effect between SO3and NH3existed through analysisand calculation, and the method of first SO3and then NH3pretreatment was morebetter to remove lignin. The reasons were that the rice straw not only reacted withSO3but also NH3, and the residual H2SO4has a chemical reaction with NH3andgenerate the small molecule. We made sure that the salt is ammonium sulfate whichcan make a large expansion to rice straw’s wall, at the same time effectivelybreaking the connection between the cellulose and hemicellulose with lignin so thatimprove the stripping of lignin effectively.(3) Finally, FT-IR, HPLC and XPS were employed to track alterations of the solidresidue and lignocellulosic hydrolyzate in the process of acid hydrolysis. Theseresults indicated that lignin with sulfuric acid had sulfonation reaction within1-5hfirstly and then lignin had phenolic condensation reaction with furfural after5h inthe process of acid hydrolysis. Because of these reactions cause the measured valueis higher than the true value of lignin. Actually, the acid hydrolysis time of1.00±0.25h was found to be suitable than2.5h for lignin determination withNational Standard of GB2677.8method.